I have two NES programs that take input up at http://hkn.berkeley.edu/~mcmartin/retro/ - tutor.nes reads up, down, and A, while Galaxy Patrol checks left, right, select, and start, at various points. The ship in Galaxy Patrol is always moving left or right, though, so if you're trying to track "no buttons pressed" it won't help much.

(Galaxy Patrol isn't really "releasable" yet because the fuel balance is still off.)

-- Michael